In this application for a Mentored Patient-Oriented Career Development Award, the candidate seeks 5 years of salary and research support to obtain further training and define the effect of vitamin D3 on markers of oxidative stress in boys with X-linked adrenoleukodystrophy (ALD; incidence 1:17,000). ALD is an inherited paroxysmal disease characterized by fatty acid accumulation and subsequent oxidative stress. Forty percent of ALD boys develop inflammatory cerebral demyelination (cerALD) in their first decade of life. Unfortunately, we have no means of identifying boys at risk for cerALD nor do we have any means of preventing the onset of cerebral ALD. These limitations represent enormous gaps in our standard of care for these patients. To address these limitations, the candidate and his collaborators consider the relationship of several key areas of current knowledge in cerALD: (1) ALD results from a peroxisomal gene defect that causes an accumulation of fatty acids which expose cells to lipid peroxides and other mediators of oxidative stress, (2) monocyte-lineage cells dominate the leading edge of the demyelinating lesions and (3) the lesions shares histologic features with multiple sclerosis lesions, a disease that has been linked to vitamin D insufficiency. Armed with this knowledge, the candidate has generated preliminary data showing that (1) low serum 25-OH vitamin D levels predict the onset of cerALD; (2) monocytes and brain myelin in ALD males have low glutathione levels compared to controls; (3) the spinal fluid from cerebral ALD boys shows a cytokine expression profile consistent with oxidative stress in monocyte-lineage cells; and lastly, (4) that oral vitamin D3 supplementation in a murine model of autoimmune demyelination significantly reduces clinical disease and increases intracellular glutathione levels in monocytes. The candidate proposes a pilot trial to study the effect of oral vitamin D3 supplementation on blood and brain biomarkers of oxidative stress in 20 ALD boys who have not yet developed cerebral ALD. In Aim 1 the candidate will use MRI techniques to monitor brain biomarkers of oxidative stress and inflammation in response to rising vitamin D levels. In Aim 2, the candidate will use 12-color flow cytometry and tandem mass spectrometry to study the effect of oral vitamin D3 supplementation on markers of oxidative stress in the specific immune cell subsets of study participants. In Aim 3, the candidate will use bio banked ALD monocytes to define the metabolic and immunologic pathways linking vitamin D exposure with glutathione and cytokine modulation. The candidate's long term goal is to develop treatments and biomarkers for the prevention of cerebral ALD. The addition of ALD to universal newborn screening panels in an increasing number of US states bolsters the project's immediate relevance.